Tests using an X-ray diagnostic apparatus include X-ray subtraction angiography. In this test, the same site of an object is taken as an image before contrast medium injection (mask image) and an image after contrast medium injection (contrast image). An image (subtraction image) obtained by calculating the difference between these images is generated.
The subtraction image is an image in which image portions of blood vessels are visualized with a contrast medium. A user can easily grasp the situation of bloodstreams in the object by observing the subtraction image. For example, in the case of thrombectomy using a catheter, it is expected to allow identification of whether bloodstreams are recovered or not in a territory of a thrombus by observing whether image portions of blood vessels downstream of a thrombus (i.e. vascular territory of the thrombus, hereinafter referred to as “territory”) appears or not in the subtraction image after thrombectomy.
For example, in thrombectomy using a catheter for a patient of cerebral infarction, an operation of removing a thrombus is tried pharmacologically by a thrombolytic agent released from the distal end of the catheter or mechanically by a device protruding from the distal end of the catheter. In this case, it is preferred that each time the operation of removing a thrombus is performed, a user as a practitioner identifies whether the bloodstream in the territory is recovered or not. This identification method may be, for example, a method of consecutively taking X-ray images while releasing the contrast medium from the distal end of the catheter into a blood vessel, obtaining subtraction images, and observing whether an image portion of the blood vessel visualized in these subtraction image appears in the territory or not.
Unfortunately, according to this method, it is difficult to determine whether the bloodstream is restored across the entire territory on the basis of the subtraction images. The difficulty is because the contrast medium released from the distal end of the catheter circulates in a bloodstream to leave normal brain tissue to be also visualized and the visualized image portion is included in the subtraction images.
The present invention has an object to provide an X-ray diagnostic apparatus, an image processing apparatus, and an image processing method capable of generating the image that allows easy identification of bloodstream recovery in the territory, i.e. in the region including blood vessels downstream of a thrombus, during or after thrombectomy using the catheter.